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Background: Black Boxes

All large commercial airplanes and some smaller airplanes are equipped with two "black boxes." One is a Cockpit Voice Recorder (CVR) and the other is a Flight Data Recorder (FDR). They record radio transmissions from the cockpit and flight information to help determine the cause of a crash. The recorders are located in the tail of the airplane, where they are most likely to survive a crash. Each recorder can survive water pressures down to 20,000 feet and are outfitted with Underwater Locator Beacons (ULB) that send out an accoustic ping at 37.5 KHz.


Cockpit Voice Recorder (CVR):
The CVR records cockpit conversations and other sounds, such as warning beeps and clicks. The microphone is located in the overhead instrument panel between the two pilots. Federal law restricts the release of any portion of the recording and only allows a written transcript to be released to the public.

Specs:
Time Recorded: 30 minutes for analog units; 2 hours for digital
Number of Channels: 4
Impact Tolerance: 3,400 G's for 6.5 milliseconds
Fire Resistance: 1,100 degrees Celsius for 30 minutes
Battery Life: 6 years of shelf life
30-day operation



Flight Data Recorder (FDR):
The FDR monitors records many different flight conditions. By law, every flight recorder must monitor at least twenty-eight important perimeters such as airspeed, altitude and heading. Some FDR's are capable of recording up to 300 perimeters. The data retrieved from these recorders allows the NTSB to generate a computer reconstruction of the flight.

Specs:
Time Recorded: up to 25 hours
Number of Perimeters: 5-300
Impact Tolerance: 3,400 G's for 6.5 milliseconds
Fire Resistance: 1,100 degrees Celsius for 30 minutes
Battery Life: 6 years of shelf life
30-day operation